This invention relates to electrostatic spray coating and more particularly to a nozzle for a powder spray gun.
In the application of powder coating material to objects in industrial finishing applications, a powder material such as an epoxy or polyester is mixed with an air carrier and is dispensed from a gun in the form of a spray which is projected toward the object to be coated. As the particulate coating material is dispensed from a gun, the particles are imparted with an electrical charge so that they will be electrostatically attracted toward the object to be coated which is generally held at ground potential. After coating, the object may be heated at bake the coating material onto its surface.
Generally, paint powder is fluidized with air and the resulting mixture is transported to a powder distribution device which disperses a plume or cloud of powder around the object to be painted. The powder containing air stream is usually contained in rubber or plastic tubing which bends easily. As the air stream travels around a bend, centrifugal force tends to force the powder toward the outside of the bend. This can result in streaming where the finely granulated material travels in a high density column in only one portion of the total air stream being used for transport. Since the powder must be evenly distributed to achieve a uniform coating, streaming is particularly objectionable when the last bend in the tube is close to the powder dispersal point.